404a high pressure?

[flyboy3b]

Sorry to jump into your posts if it's not entirely concluded yet but it appears to be getting close now.

youre not intruding at all. isnt that what this forum is all about?

[Gary]

evap air in (from the intake) 38f

Judging from the previous evap delta-T's, the evap air in (at the coil) would be about 48F, so we can estimate that the return duct is gaining at least 10F (48 - 38 = 10F gain). That's a HUGE gain.

You really need to do something about the return air duct. It needs to be leak-free and very heavily insulated. The temp at each end of that duct should be nearly identical.

Possibly the heat gain is coming from the evaporator compartment itself, so the compartment should be leak-free and heavily insulated also.

A lot of heat is getting in somewhere.

[flyboy3b]

You really need to do something about the return air duct. It needs to be leak-free and very heavily insulated. The temp at each end of that duct should be nearly identical.

i was thinking it might be better to just eliminate the return duct and enlarge the evaporator chamber. (basically just hang the coil in the cooler space,,, so to speak). that would eliminate any chance of other air leaking in. give me a couple days to think about some other options,, and to let the cooler settle down,, and ill repost the current results.
one thing i notice,, when im taking the evap air out temp,,, is how fast that temperature rises when i open the door. there should be no negative or positive pressure difference inside the box, but it sure seems to draw outside air in fast when i open the door.

anyhow,, till next time,
thanks,
mike

[Gary]

Hi Gary, before Nike 123 posted his interesting observation, I was just thinking to myself, the tremendous job you had done in guiding FlyBoy through this project thus far.

However, the downside ... I fear it will impact your book sales !!

Why? because you have (kindly) divulged most of your knacks and techniques over the course of this 77+ post thread. . Many of the newbies may have all they need ( if they are sharp on the uptake!)

kind regards
T-P

I would like to think that this thread has been helpful to many people, but it is in fact just a small taste of what's in my books.

[nike123]

Just to point out, my previous observation has nothing to do with content of this thread. It is just observation that this is longest thread of this forum.

[knight rider]

IF I COULD I WOULD VOTE FOR GRAY USA PRESIDENT

and i am gone buy a set off his books ,

[Gary]

IF I COULD I WOULD VOTE FOR GRAY USA PRESIDENT

Hmmm... on day one I would issue a presidential pardon to all non-violent drug offenders.

On day two I would pardon all tax evaders.

On day three I would be assassinated... LOL

[thermo prince]

Hi again Gary, Knight rider .... a good man to run no doubt but bad address.
FLORIDA - hmmmm was'nt that where all the fun occurred last time ?
Florida, President-elects, Governors, re-counts, hanging chads
If you wanna run, could you not temporarily move 'next door' to like Tennessee or the Carolinas for a while? LOL !

Hi Nike 123 - sorry I did not mean to imply you made any observation regarding content in a positive/negative light whatsoever - I simply referred to your observation of the post count( at 77) thus far in making my follow -on comment !

best regards
T-P

[flyboy3b]

IF I COULD I WOULD VOTE FOR GRAY USA PRESIDENT

and i am gone buy a set off his books ,

gary, can we legalize homebuilt distilleries?

[Gary]

gary, can we legalize homebuilt distilleries?

Yep... but if you poison anyone (other than yourself) you're in big trouble.

[flyboy3b]

Yep... but if you poison anyone (other than yourself) you're in big trouble.

you sound like one of those non-believers. i could no more poison you with homemade rum,, than you could poison me with ditch weed.

one of the common misconceptions with home brew is poisoning. now,, there were moonshiners back in prohibition that would add things to "thin" out their brew,,, and the government makes us add poison to make rubbing alcohol undrinkable (denatured). but distilling is a purifying process where bad things are removed. and there arent alot of bad things to begin with,, mostly stuff that tastes funny, and you would have to drink a whole lot of those bad things to even get sick (and youd probably get sick from the alcohol first).

george washington was a big proponent of home distilling and he thought everyone should have one in their yard.

do i sound fanatical??

[Gary]

What is "ditch weed"?

[flyboy3b]

Hmmm... on day one I would issue a presidential pardon to all non-violent drug offenders.

its street language for homegrown pot

[Gary]

its street language for homegrown pot

I never use the stuff... and I rarely use alcohol. But if others want to use all of the above, I have no right to stop them. I have a simple philosophy: If you want to smack yourself in the head... it's your head.

If you want to smack someone else's head, that's a different story. The legitimate basis of government is collective self defense.

[TRASH101]

A flawed philosophy I`m afraid

someone may get smacked in the head and then blame you.

someone might pretend to get smacked in the head and blame you.

you might try and smack yourself in the head miss and hit the person beside you.

But in essence a really sound philosophy

[flyboy3b]

I have a simple philosophy: If you want to smack yourself in the head... it's your head.

i am enjoying my new hobby of home distillation and it pleases me no end that i can make something that tastes better and is cleaner than what i can buy in the store. everything in moderation i guess. anyhow,, i have a different forum for home distillation so ill get back to things at hand...

ambient 75f
box 44f
cond air in 75f
cond air out 91f
evap air in 53
evap air out 41f
suction at bulb 32f
suction at compressor 53f
liquid at receiver 104f
pressures at 60/295 psig

this leaves me with 11f superheat and 12f subcooling. the txv was wandering between 29f and 32f bulb temperature and seemed pretty normal. the unit may be a bit overcharged.

at this point, i think, once i get the evaporator air in temperature down about 6 or 7 degrees i will need to increase the superheat a couple of turns which should lower the pressure a tad and bring the evaporator air out temp down 1 or 2 degrees. otherwise,, we are in the ballpark.

gary,, once again,, i thank you for your time and patience. and of course to everyone else who shared thier ideas. i have started to read the manuals i got from you and im waiting for the next time i can try out the TECH system (which may be sooner than later, i had my manitowoc ice machine apart this morning and it was flashing an error code that the harvest cycle had exceeded 3 1/2 minutes 3 times) i reset the machine and watched it through 3 cycles with no problem).

itll be a bit before i can tear that wine cooler apart to redo the air intake,, but ill keep you posted as to the results.

to summarize,,, (and please correct me if im wrong)...

the original question was "how do i know when i have the charge right in a medium temp home built system"

the answer is,,,

add refrigerant until the subcooling reaches around 15f.
keep the superheat between 20f and 30f
keep the delta t for the condenser to less than 30f
keep the delta t for the evaporator less than 20f
assuming that everything else seems normal, the charge is correct.

[Gary]

A flawed philosophy I`m afraid

someone may get smacked in the head and then blame you.

someone might pretend to get smacked in the head and blame you.

you might try and smack yourself in the head miss and hit the person beside you.

But in essence a really sound philosophy

Hmmm... perjury should be illegal... perjury should be illegal... accidents happen, you pay for the damages you cause.

[Gary]

The charge is enough to do the job, but you might add just a little more refrigerant to bring the subcooling up to 15F.

The superheat looks just right... leave it alone.

The condenser TD is a little high, but I stopped believing the cond air in temp a long time ago and we know the condenser is not in an ideal spot.

The evaporator TD is high, but that's because it doesn't have much surface area. It's not like a real evaporator... lol

The major problem at this point is the return air.

Everything else is looking pretty good... considering.

[flyboy3b]

okey dokey,, here we go again. yesterday the cooler had warmed up. i pulled it apart and hooked up my gauges. the low pressure was way high. like 90 psig and the high side was normal at around 300 psig. i adjusted the txv all the way down and the pressure dropped and i could hear the refrigerant when i opened it back up again.

so this morning i rechecked it, i did a leak check on it, pumped it down to rule out noncondensibles and i refilled it. there was no change so i closed off the receiver valve and it pumped down to 10 inches of vacuum which it held for at least 20 mins.

im thinking its the txv, but its brand new. any thought on this matter would be appreciated.
thanks,
mike

[flyboy3b]

and as an after thought. what condition might cause a txv to fail? its like the spring is broken or the valve is stuck.

[Gary]

okey dokey,, here we go again. yesterday the cooler had warmed up. i pulled it apart and hooked up my gauges. the low pressure was way high. like 90 psig and the high side was normal at around 300 psig.

And you didn't take readings to find out what was wrong?

[Gary]

and as an after thought. what condition might cause a txv to fail? its like the spring is broken or the valve is stuck.

There is nothing wrong with the TXV and it was adjusted just right. At that point it should have been put under lock and key and throw away the key so you couldn't mess with it... ever again.

Once a TXV is adjusted it should never need to be adjusted again. There is a long list of things that can go wrong with a system. The TXV is never at the top of the list, it is at the very bottom of the list. Eliminate all other possible problems before suspecting or adjusting the TXV.

[Gary]

there was no change so i closed off the receiver valve and it pumped down to 10 inches of vacuum which it held for at least 20 mins.

The compressor should be able to pump at least 15 inches of vacuum.

Remember back when I said the suction line should come out of the coil, down then up (oil trap), to the top of the coil and back down (reverse trap), then to the compressor?

The coil will gather liquid during the off cycle. If the suction line goes straight down to the compressor then gravity can fill the compressor crankcase with liquid. The compressor then starts, washes out the oil and tries to pump liquid, which can break the compressor valves. The reverse trap prevents this. You did install the traps, right?

[flyboy3b]

i didnt see much point in taking all the temps. the box was warm,, the evap air in and out was warm. the air going in and out of the condenser was warm the liquid line was warmer,, but not hot. i have no idea of what the superheat was,, but i with the pressure being so high,, i didnt see much point in checking. i have three trouble shooting manuals,, including your own and i cant find anything that diagnoses a box with high high side pressure, very high low side pressure and everything is warm.

[flyboy3b]

The compressor should be able to pump at least 15 inches of vacuum.

Remember back when I said the suction line should come out of the coil,

maybe my guage is off by 5 lbs,, i dont know,, but would it make that much difference (cold one day and warm the next)?

and i did put that loop in the suction line

[Gary]

The high side pressure is elevated because you have the condenser boxed in and trapped up against a wall. The hot air is recirculating.

[flyboy3b]

maybe you dont understand,,,

everything is warm

something is wrong ,,, the cooler has been in the same place since i installed it and it was cooling before,, and now its not.

[Gary]

Take readings.

[flyboy3b]

the soonest i can get back in there now will be this afternoon,, if its not busy,, otherwise ill be working on it tomorrow

[Gary]

i have three trouble shooting manuals, including your own and i cant find anything that diagnoses a box with high high side pressure, very high low side pressure and everything is warm.

Elevated high side pressure tells you absolutely nothing. Elevated low side pressure tells you absolutely nothing. Everything is warm tells you absolutely nothing.

The TECH Method procedure is sequential. Do not pass go, do not jump to the pressures, do not jump to the TXV, do not jump to non-condensables, do not jump at all.

Follow the procedure step by step.

[flyboy3b]

Do not pass go, do not jump to the pressures, do not jump to the TXV, do not jump to non-condensables, do not jump at all.

Follow the procedure step by step.

i didnt jump to anything. i felt every line, i felt the txv, i felt the temp in the inside of the cooler. then i thought about it last night,, and did some reading.

this morning, i checked it again. everything was warm. the low side pressure was 90 psig. so i tapped on the txv,, thinking it might have been stuck. the high side pressure seemed normal and the liquid line was warm (i felt the same as any other time ive checked it). so i tried a valve test by closing the receiver valve. the results from that seemed within range. now,, i asked myself,, i said "self",,, " what else could cause the low side pressure to be so high in just one day" and myself replied,,, "it must be the txv". so i adjusted it down one full turn at a time,, and the pressure didnt change until it was almost closed. one more half turn and the txv closed.

i just took these readings with the txv back in the middle,,,

suction line at bulb 68f
suction line at compressor 68f
liquid line at receiver 96f
cond air in 74f
cond air out 90f
evap air in 69f
evap air out 68f
ambient 77f
bos 77f
pressures at 85 and 270 psig
14f subcooling
28f superheat

[tonyelian]

hi flyboy
first of all you have to check your comp
i have adjust the txv all the way down so i think your low side should show a lowest reading
in my point of view all your readings from the first post the low &high side are high its winter time & what would you do in summer time you should see these reading in the most hottest days
in my opinion your major problem came from 3 things
1-expansion device
2-evaporator fan speed
3-insulation your box-air leakeage-design of air circulation in your box
your compressor is a lbp application &it suffer to much so if it still alive try to switch to a cap. tube&you will see the difference your project needs a little change &worth to do it after 180 posts.

[flyboy3b]

what would you do in summer time you should see these reading in the most hottest days
in my opinion your major problem came from 3 things
1-expansion device
2-evaporator fan speed
3-insulation your box-air leakeage-design of air circulation in your box
your compressor is a lbp application &it suffer to much so if it still alive try to switch to a cap. tube&you will see the difference your project needs a little change &worth to do it after 180 posts.

i agree,, i may have to change the configuration in the summer. i can always go to a remote condensing unit, but i will wait and see how it does. i started this cooler out with a cap tube and a different compressor using 134a. it didnt have enough capacity for the space. but perhaps this compressor might be better suited for the cap tube.

it should run with what is has in it,, so i will try that first,, but i thank you for your advice.
mike

[Gary]

Is the return duct disconnected? It acts like it is sucking in nothing but room air.

[Gary]

i asked myself,, i said "self",,, " what else could cause the low side pressure to be so high in just one day" and myself replied,,, "it must be the txv". so i adjusted it down one full turn at a time,, and the pressure didnt change until it was almost closed. one more half turn and the txv closed.

The TXV doesn't control the low side pressure, it controls the superheat. The low side pressure is about temperatures.

[flyboy3b]

The TXV doesn't control the low side pressure, it controls the superheat. The low side pressure is about temperatures.

i understand that it controls the superheat, but how come when i adjust the txv,, the low side pressure changes?

and no,, the air intake is the same. as far as i know,, everything is the same. i really think this is a mechanical failure.

[Gary]

If the TXV were overfeeding, the result would be low superheat. The superheat is not low.

[flyboy3b]

but why is the pressure so high then? all of a sudden like.

[flyboy3b]

if there were access valves on either side of the txv,, theoretically the pressures should about 50 and 300 for this system (thereabouts). it seems to me that the txv is not doing its job by regulating the pressure correctly?

[Gary]

Why is the evap delta-T only 1F? I suspect the actual evap air in temp is much higher than 69F. Could air be leaking in around the sides of the evaporator chamber?

[Gary]

if there were access valves on either side of the txv,, theoretically the pressures should about 50 and 300 for this system (thereabouts). it seems to me that the txv is not doing its job by regulating the pressure correctly?

There are no "should be" pressures. The pressures depend upon the temperature and volume of airflow entering the coils, as well as the pumping efficiency of the compressor... and the TXV's job is to regulate the superheat, not the pressure.

[flyboy3b]

Why is the evap delta-T only 1F? I suspect the actual evap air in temp is much higher than 69F. Could air be leaking in around the sides of the evaporator chamber?

the delta-t is low because there is NO cold air,,, its all the same temp. the txv is barely cold. ive looked at that chamber a bunch of times now. besides,, it was fine a day ago. its been fine since i replaced the txv.

i guess i learned that there needs to be a pressure drop in order for there to be cooling,, and the txv is where that pressure drop happens. so if the pressure before the txv is right,, then the txv isnt doing its job in dropping the pressure sufficiently. if i were to adjust the txv to almost closed,, the pressure would be fine but there would be no refrigerant flow.

am i wrong here in this understanding?

[Gary]

On the high side the pressure needs to correspond to a temperature that is higher than the temperature of the air entering the condenser, so that the heat will transfer from the refrigerant to the air.

On the low side the pressure needs to correspond to a temperature that is lower than the temperature of the air entering the evaporator, so that the heat will transfer from the air to the refrigerant.

You are confusing yourself with pressures. Refrigeration is about temperatures and heat transfer. It is not about pressures. The only reason you put gauges on the system is to determine the saturation temperatures.

The evaporating temperature aka saturated suction temperature (SST) is about 40F. The air entering the evap is 69F. Heat is transferred between the air and the refrigerant, therefore the temperature of the leaving air should be much lower... OR... the temperature of the air entering the evaporator is in fact much higher than 69F.

[flyboy3b]

The only reason you put gauges on the system is to determine the saturation temperatures.

well,, the day before yesterday,, that gauge read 50 psig,,and the temperature was 42 and now it isnt,, and the box is the same.

[Gary]

The day before yesterday, the difference between the leaving air temp and the SST was about 28F (approach). Now the approach is about 27F. So the heat transfer is about the same. But the day before yesterday the air in temp was 53F. Now it is 69F... and if the heat transfer is the same, then the air in temp must be much higher than 69F. Something changed. Whatever has been heating the return air got worse.

[Gary]

The day before yesterday the delta-T was 12F. Today it is 1F. If the approach is the same then the actual delta-T should be about the same. If the delta-T is the same, then the actual air in temp is about 80F, not 69F.

[flyboy3b]

ill look at more in the morning,, see if i can see any other cause. i really dont see anything different at this point.

and thanks again for your time,
mike

[Gary]

Describe the return duct for us. Is it metal?... plastic?... insulated?

At the very least it should be insulated flexduct, such as used for A/C systems.

The evaporator chamber itself should also be sealed and insulated.

Notice the construction of the box. It is double wall with insulation in between. Insulation is important.

[Gary]

Another thing I noticed while looking at the pictures: The evaporator coil is right up against the fan. There should be a space in between them to draw air evenly through the coil.

[flyboy3b]

Describe the return duct for us. Is it metal?... plastic?... insulated?

At the very least it should be insulated flexduct, such as used for A/C systems.

The evaporator chamber itself should also be sealed and insulated.

Notice the construction of the box. It is double wall with insulation in between. Insulation is important.

the duct is basically 2 - 6" galvanized elbows going from the side of the box to the bottom of the evap chamber and it is insulated.

the box is 3/4" birch plywood with 1" foil covered foam insulation sandwiched in between. the doors are double glazed with a 1/2" space between.

the evap chamber is 3/4" plywood with 1 1/2 " stryofoam on the top and right side (the left side borders the cooler) and 1" foil covered foam in the back. the bottom is just plywood.

i built my back bar cooler and its the same construction and much larger and the condensing unit is the same size as the wine cooler. the back bar cooler has been working fine for almost 4 years.

Another thing I noticed while looking at the pictures: The evaporator coil is right up against the fan. There should be a space in between them to draw air evenly through the coil.

there is a couple of inches between the fan and the coil.

anyhow,, i checked it this morning,, and it has started cooling again and im confused. i understand that the pressures are relative to the temperatures of the ambient air, air flow, and box temperatures. but,,,,

the ambient temps have been basically the same this whole time.

even when the box was warm, the txv would still frost up.

even though the superheat was really high the txv would still frost up.

through this whole thing,, the low side pressure had never been this high.

anyhow,, here are the new readings,,,

ambient 76f
box 52f
suction line at bulb 42f
suction at compressor 51f
liquid line at receiver 97f
cond air in 77f... out 86f
evap air in 53f... out 44f
pressures at 60 and 270 psig
superheat 19f
subcooling 16f

and yes,, i agree that there are inefficiencies in this sytem, but that doesnt explain the huge difference over the last couple of days.